Photographic materials



atented Apr. 23, W48

PHOTGGRAPHEC MATERIALS No Drawing. Application February 10, 1943, Se-

rial No. 475,436; In Great ritain February 13,

Claims.

This invention relates to light sensitive photographic materials and particularly to the pro,- duction of photographic silver halide emulsions of increased light sensitivity.

Processes have been known for many years wherein the colour of the images obtained from print out emulsions (i. e. emulsions which form an image, merely on exposure to light and without recourse to chemical development) has been toned by treating the prints obtained with solutions of gold salts or by including gold salts in the emulsions.

It has also been proposed, for example in British Patent No. 417,257, to tone the image-colour of prints obtained from silver chloride development emulsions by including gold salts in such emulsions.

In the production of gelatino silver halide development emulsions as normally'practised, it is usual after forming the silver halide emulsion in a gelatinmedium, to ripen it, set it, wash it and then digest it before coating. The washing operation removes the soluble salts formed in the preparation of the silver halide and the digestion operation further increases the speed of the final emulsion.

It has now been discovered, and this, forms ,the

' basis of the present invention, that the addition of small quantities of soluble gold salts to gelatino silver halide photographic emulsions (the principal halide present being silver bromide) prior to or during the digestion of such emulsions, and preferably while the emulsions have a pH value not greater than about 8, results in a very considerable increase in the light sensitivity of the final emulsions.

It is now generally accepted that all normal gelatin contain small proportions of sulphur compounds such as thiosinamine or allyl isothiocyanate and it is believed that the presence of such sulphur compounds'is essential if the best results are to be obtained by the process of this invention since it is found that those modern gelatins known as inert benefit by an addition of a small quantity of such a compound. .Acoordingly, the gelatino silver halide emulsions em-' ployed should contain such sulphur compounds either as natural constituents of the gelatin or as positive additions. For optimum results the positive addition of a sulphur compound is often but not always necessary, e. g. an allyl isothiocyanata.

thio-urea or an N-substituted thio-urea such as thiosinamine. Improvement in the results can also be effected by including small quantities of an alkali or ammonium thiocyanate with the gold salt.

The invention may be applied to emulsions in which the silver halide present is wholly silver example, potassium aurate, potassium chloraurite, potassium bromaurite, potassium iodoaurite, potassium iodoaurate, potassium auricyanide and potassium aurithiocyanate, or the corresponding sodium, calcium, strontium, cadmium or gallium salts. Complex organic gold salts may also be used, e. g. pyridino-trichlorogold, ethylene-diamine-bis-trichloro-gold, di-

ethyl-monobrom-gold and diethyl-gold-acetyl- 2 acetone, and also the gold complexes with sulphur compounds such as thiourea, and with the sulphur compounds commonly present in gelatin,

e. g. thegold thiosinamine complexes.

its indicated above, the quantity of gold salt employed is necessarily very small, much smaller than would make any appreciable difierence to the tone of the image obtained from the emulsions. If too much gold salt is employed the full speed increase is not obtained. The precise quantities of gold salt will, of course, depend on the nature of the gold salt itself and on the nature of the emulsionto which it is added. However, for an emulsion of normal silver halide content, e. g. 2-3%, calculated as-metallic silver, a quansion is important and it has been found that the best results are obtained (especially in the case of panchromatic emulsions) it the pH value of ,the emulsion both during digestion and during coating is maintained below about pH 8. By-

keeping the emulsion on the acid side of neutrality, more uniform results are obtained from bromide or to emulsions which also contain smallbut any other soluble gold salt may be used, for

tity varying from 1 cc. to 50 ccs. or up to ccs. of a 1 in 10,000solution of sodium chloroaurate successive batches of emulsion and the increase in speed of theflnal emulsion is greater.

The following examples illustrate the invention but are not to be regarded as limiting it in any way:

Exmra I- (a) One litre of a gelatino-silver iodobromide emulsion having a silver halide (principally silver bromide) content of 25 gmacalculated as silver, was digested under conditions leading to the maximum speed in the final emulsion but without causing any appreciable fogging of the emulsion. Further gelatin was added and the emulsion was coated on glass and dried. On testing the speed of the emulsion to white light it was found that the emulsion had a relative speed (b) To 1 litre of the same emulsion as in (a) 6 ccs. of a 1:10.000 solution of sodium chloroaurate was added before digestion. The emulsion was then treated as before and on testing the speed of the emulsion to white light, it was found to ExAmrLn II This example illustrates the eil'ect of the pH value of the emulsion during digestion and during coating on the speed of the final emulsion ob tained.

(a) An emulsion was prepared as in Example I (a), the pH of the emulsion at the digestion stage being 8.3 and at the coating stage 6.9. The speed of the emulsion to white light was found to have a relative value of 38. i

(b) 1 litre from the same emulsion was prepared as in (a) above and '7 ccs. oi a 1:10.000 solution of sodium chloroaurate was added before digestion. This addition did not affect the pH value of the emulsion during digestion or coating, which remained at 8.3 and 6.9 respectively. The

.speed of the final emulsion to white light was Exmrs III (a) one we of a gelatino-silver iodobromide emulsion having a silver halide (principally silver bromide) content equivalent to 28.5 ems. caloulated as silver, and colour-sensitised by the addition of (1.3.3.4rimethyl-indolylidene) -2.4'-

- ethylidene-(l' phenyl 3' methyl pyrazole-5'- orielfwa digestedjto give optimum speed in the emulsion. Afurther quantity of gelatin was add F a'nd the emulsion was coated and dried.

The resulting emulsion was found to have a relative speed value to white light of I2.

. (b) 1 litre from the same emulsion prepared.

asin (a) above was modified by the addition of 6 cos. of a 1:10.000 solution of sodium chl010-- aurate before digestion. The speed or the final emulsion to white light was ative valueof 130.

(c) 1 litre from the same emulsion as in (a) above was modified by the addition 01' 1 cc. of a found to have a rel- 1:10,000 solution of thiosinamine before setting and the addition of 9 cos. of a, 1:l0,000 solution of sodium aurichlorlde before digestion.

. The final emulsion wa found to have a relative speed to white light of 150.

EXAMPLE IV 4 (a) One litre of a panchromaticallysensitised gelatino-silver iodobromide'emulsion having a silver halide (principally silver bromide) content equivalent to 28.5 gms. calculated as silver, was

digested to give the greatest possible speed. Further gelatin was added and the emulsion was coated and dried. During digestion the pH value v of this emulsion was 7.9 and during coating'was 6.95. The speed of the coated and dried emulsion to white light was found to have a relative value oi 130. I

(b) 1 litre from the sameemulsion wa prepared as in (a) above with the modification that 6 ccs. of a 1:10.000 solution of sodium chloroaurate and 7 ccs. of normal hydrochloric acid were added before digestion. The pH value during dgestion then became 5.7 and during coating 6.0. The relative speed value of the coated and dried emulsion was found to be 340.

EXAMPLE V pared as in (b) above except that 1.71 cos. of a 1:10.000 solution of potassium thiocyanate was added (in addition to the 3.2 cos. of a 1:10.000 solution of sodium chloraurate and the 7 cos. of normal hydrochloric acid) immediately before digestion. The relative speed value of the final emulsion obtained was found to be 390.

Example VI Five litres of a gelatino silver iodobromidem emulsion having a silver halide (chiefly silver bromide) content equivalent to 142.5 gins. calculated as silver was dividedinto five parts. The first part (a) was digested atpH 8.3 to optimum speed and coated at pH 6.9. The remaining four parts, (0), (c). (d) and (e), were adjusted to pH 6.3, gold salt addition were made before digestion,

and the several parts coated at pH value about 6.6. The results obtained are shown in the following table.

Table Relative Gold salt speed I a hill -50 o 0 cc. 130,000 pyridine trlcliloro gold U c 5 oc. 1:10.000 ethylene diamino bis-trichloro-gold-.;. 160' d) 4 cc. 1:10.000 potamium aunts... 21m e) Bee. 1:10.000 potassium chloroaurite 2oz) AZPLE VII 01) An emulsion was prepared as in Enample I (a) the :13 during digestion being adiusted to aseaoss 5.95. On testing the speed of the emulsion to white light, it was found that the a, relative speed of 42.

,(b) To 1 litre of the same emulsion as in (a), 4 cos. of a 1:10,000 solution of aurous bisthlo carbamide chloride was added before digestion. The emulsion was then treated as before and on testing the speed of the emulsion to white light it was found to have a relative speed of 63.

What we claim is:

1. In a process of producing gelatino-silver halide emulsion layers which predominate in silver bromide and contain "a sulfur sensitizer, including precipitation, washing and digestion stages and coating; the step which comprises digesting such emulsions on the acid side of nell-' trality in the presence of a small amount of a soluble gold salt which is smaller than that which would make any appreciable difference to the tone of the developed silver images obtained from the emulsions, and coating said emulsions emulsion had 1 to 100 cc. of a 1 to 10,000 solution of such salt, and coating said emulsions on a support while maintaining the emulsions on the acid side of neutrality.

3. In a process of producing gelatino-silver halide emulsion layers which predominate in silver bromide and contain a sulfur sensitizer, including precipitation. washing and digestion stages and coating; the step which comprises digesting such emulsions on the acid side of neutrality in the presence of a small amount of sodium chloroaurate which is smaller than that which would make any appreciable difference to the tone of the developed silver images obtained from the emulsions, and coating said emulsions on a support while maintaining the emulsions on the acid side of neutrality.

4. In a process of producing gelatino-silver on a support while maintaining the emulsions gold salt per liter of emulsion equal to that in bromide and contain a sulfur sensitizer, including precipitation; washing and digestion stages and coating; the step which comprises digesting such emulsions on the acid side of neutrality in the presence of an amount of sodium chloroaurate per liter of emulsion equal to that in 1 tov 100 cc. of a 1 to 10,000 solution ofsuch salt, and coating said emulsions on a support while maintaining the emulsions'on the acid side of neutrality.

5. The product of the process of claim 1.

CECIL WALLER.

RONALD BERNARD COLLINS. EDWARD CYRIL DODD. 

